Secondary fiber has long served as a source of raw fiber material in papermaking. The recycling of secondary fiber continues to increase. Secondary fiber must be processed to remove the ink to permit the manufacture of high quality paper. For years paper was printed with primarily water or oil-based inks which were satisfactorily removed by conventional deinking procedures. In conventional deinking procedures, secondary fiber is mechanically pulped and contacted with an aqueous medium containing a surfactant. The mechanical pulping and the action of the surfactant result in separation of the ink from the pulp fibers. The dispersed ink is then separated from the pulp fibers by processes such as washing or flotation.
Increasing amounts of secondary fiber are generated from reprographic printing processes such as electrophotographic copying, e.g., xerography, and nonimpact printing, e.g., laser or ink-jet printing. The difficulty in the deinking of xerographically printed secondary fiber has been attributed to the binder of the xerographic ink, which is different from those in common oil-based inks. The xerographic-ink binder is typically a polymeric material which is thermally fixed to the paper. Xerographic-ink binders are not easily dispersed by commonly used surfactants such as nonylphenol ethoxylate. As a result, paper produced from xerographic secondary fiber has a high dirt count, i.e., the paper contains visible ink particles and is a lower grade product.
Often reprographic processes, such as xerography, utilize magnetic inks or magnetic toners. Such magnetic ink also generally includes a polymeric binder that is not effectively removed by conventional deinking procedures. The increasing abundance of secondary fiber containing magnetic ink has made the reclamation of such secondary fiber economically attractive. Yet, the inability to remove magnetic ink from secondary fiber has limited the recycle of such secondary fiber to low-grade paper products.
It is therefore the principal object of this invention to provide a method of deinking secondary fiber printed by reprographic printing processes to provide a deinked pulp suitable for producing paper comparable in quality to paper prepared from virgin pulp.